Direct-contact steam-to-water condenser

ABSTRACT

Apparatus that uses a supply of superheated steam to heat a supply of white water and optionally one or more supplies of clean water by means of heat exchangers. The heat exchanger used to heat the white water uses baffle trays to accommodate the contaminants in the white water.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to processes orfacilities that both produce superheated steam and use one or moresources of water wherein one water source has material suspendedtherein. More particularly, the present invention relates to capturingheat from such superheated steam and then using the energy to heat theone or more sources of water.

[0003] 2. Description of Related Art

[0004] Many manufacturing processes require supplied water, and often itis necessary or desirable for this water to be heated. From an economicstandpoint it is best to use waste heat—that is heat which is producedfrom the manufacturing process, as opposed to for it—to heat the water.During such manufacturing processes, the supplied water often becomescontaminated with solids or chemicals, and, notwithstanding thiscontamination, is reused for its original or an alternative purpose. Aproblem arises in using waste heat to heat supplies of contaminatedwater: solids in the contaminated water tend to foul (plug) certaintypes of heat exchanges used to effect the heating.

[0005] Few attempts have been made to use an abundant supply of wasteheat to heat the supply of contaminated water. (In certain fields thiscontaminated water is referred to as “whitewater.”) An apparatus andprocess for drying cellulosic and textile substances with superheatedsteam is taught by Curry (U.S. Pat. No. 5,105,558; 1992). The apparatusof Curry uses superheated steam as a medium to dry cellulosic goods, andcontains an internal steam condenser for recapturing the energy of thesteam after the steam has been used for drying the goods. Whileproviding for an efficient method of drying pulp goods and recapturingthe energy of spent steam, the Curry apparatus fails to provide a methodand structure with which to use this heat energy advantageously to heatthe whitewater produced in the initial stages of the molding process.

[0006] A similar apparatus and method are taught by Stubbing (U.S. Pat.No. 5,711,086; 1998). The Stubbing apparatus, like that of Curry, usessuperheated steam as a drying medium and has a condenser to capture heatfrom the spent steam. The Stubbing apparatus, like that of Curry, failsto provide for the heating of dual production liquid supplies where oneof the supplies has by-product in suspension.

[0007] A waste water heat recovery apparatus is taught by MacKelvie(U.S. Pat. No. 5,736,059; 1998). The MacKelvie apparatus employs athree-fluid convective heat exchanger that transfers heat from wastewater to a fresh water supply indirectly via a reservoir of fresh water.Certain embodiments of the MacKelvie apparatus contain a solidsseparator to remove particulate matter from the waste water supply. TheMacKelvie apparatus uses waste water to heat the fresh water supply fora house or other such building. Because of the paramount need to keepthe supply of fresh water potable, an indirect heat exchanger isnecessary; the waste water supply can never, barring the rupture of bothsupply pipes, come into contact with the fresh water supply. Suchindirect heat exchanges, particularly those with an intermediatefluid—as is the case with the MacKelvie heat exchanger—are inherentlyless efficient than direct heat exchanges, i.e., heat exchanges whereinthe input and output fluids mix directly.

[0008] A wet/dry steam condenser is taught by Brigada et al. (“Brigada”)(U.S. Pat. No. 4,381,817; 1983). The apparatus of Brigada uses aplurality of substantially vertical pipes (“heat pipes”) and thatcontain a heat transfer liquid. Steam is collected and directed to thelower end of the heat pipes, causing the heat transfer liquid tovaporize within the pipes. Cooling air, and in some embodiments coolingwater, carry away heat from the sealed heat pipes, causing the vaporizedheat transfer liquid to condense. The step of vaporizing the heattransfer liquid removes energy from the steam, and causes the steam tocondense to liquid water. The Brigada apparatus uses an indirect heatexchanger wherein the steam supply and the fluid that ultimately carriesaway the extracted heat energy are separated by an intermediary andenclosed fluid, and because of this the inefficiencies inherent in suchheat exchanges are present. Moreover, the Brigada apparatus provides nostructure with which to use the heat that is extracted from the steam;the apparatus is directed to condensing steam, and not to beneficiallyusing the extracted thermal energy.

[0009] In light of the limitations described above, what is neededtherefore, is an apparatus

[0010] In light of the limitations described above, what is neededtherefore, is an apparatus that is capable of transferring heat from asupply of superheated steam to one or more supplies of water, where onesuch supply is whitewater with manufacturing by-products therein.

SUMMARY OF THE PRESENT INVENTION

[0011] The present invention solves the problem of heating a supply ofwhitewater with waste heat while accommodating the manufacturingby-products in the whitewater by use of a whitewater heat exchanger thathas multiple baffle trays which accommodate the manufacturingby-products in the whitewater.

[0012] When superheated steam is produced in a manufacturing process andis subsequently vented unused to the atmosphere, economically valuablethermal energy that might otherwise be beneficially used is wasted. Thissuperheated steam represents a source of energy with which to heat otherfluids used in the manufacturing process. The most common among thesefluids are water and “white water.” White water, as previously noted,refers to water that contains by-products of the particularmanufacturing process. The problem with using this superheated steam toheat supplies of such whitewater is that the solid materials containedin the whitewater eventually plug most types of heat exchangers. Thepresent invention solves this problem and provides for the use of wasteheat contained in a supply of exhausted superheated steam to heat one ormore supplies of water, one supply containing suspended material.

[0013] As used herein “superheated steam” refers to steam at a pressureof about one atmosphere which is heated above the saturationtemperature; “superheated steam” may also refer to any mixture of suchsteam with air. Furthermore, the term “freshwater” includes reference toany supply of water, whether from municipal, groundwater, or surfacesources, that is suitable for a particular manufacturing process andwhich has not been contaminated with manufacturing by-product(s).

[0014] An essential aspect of the present invention is the presence of adirect-contact heat exchanger assembly with which to heat a supply ofwhitewater, the “whitewater heat exchanger,” which is capable ofaccommodating the suspended solids of the supply of whitewater; thiswhitewater heat exchanger is able to function despite the presences ofsolid material in suspension in the whitewater. This functionality isprovided by baffle trays within the whitewater heat exchanger whichfilter the suspended material while still allowing the superheated steamto pass through the whitewater heat exchanger.

[0015] The present invention includes classes of embodiments that useonly one heat exchanger, for a single whitewater supply; the presentinvention further includes classes of embodiments that use two or moreheat exchangers, one of the heat exchangers being for a white watersupply and the remaining heat exchanger(s) being for non-whitewatersupplies The heat exchangers of the present invention are of thedirect-contact type: the steam comes into direct contact (i.e., directlymixes) with the water and no barrier separate the two fluids. In mosttypes of heat exchanges, a barrier is present between the fluids. Thisbarrier is most commonly metal. However, this barrier presents aresistance to heat transfer regardless of the type of material use forthe barrier. For optimum heat transfer between the steam and water,barrier walls are done away with in the present invention.

[0016] Superheated steam from a steam source enters a steam inlet of theapparatus of the present invention and is directed to the whitewaterheat exchanger. If it is the case that a freshwater supply is to beheated as well, there will be a forked plenum (manifold) that directssome of the superheated steam to a freshwater heat exchanger. In bothtypes of heat exchanger, the water supply enters the heat exchangerabove where the superheated steam enters (the “superheated steam inlet”)and exits below this superheated steam inlet; the superheated steam inboth types of heat exchanger exits above the water inlet. Thisarrangement provides for optimal heat transfer between the fluids; thesuperheated steam rising up through the heat exchanger and being cooledby the falling water while the water is simultaneously heated as itcomes into contact with the rising superheated steam.

[0017] While the present invention described in the following PreferredEmbodiment is directed to use in the process of making paper-pulp-goods,the scope of the present invention is not limited to that singleapplication. Indeed, the present invention may be used in any processwhere (1) superheated steam as well as white water are produced, and (2)it is desired to heat such whitewater.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows a front view of the Preferred Embodiment of thepresent invention wherein a superheated steam inlet is connected to awhite water heat exchanger and a fresh water heat exchanger.

[0019]FIG. 2 shows a sectional side view of the white water heatexchanger of the Preferred Embodiment of the present invention.

[0020]FIG. 3 shows a plan view of a baffle tray of the white water heatexchanger.

[0021]FIG. 4 shows an edge view of a baffle tray.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The following description of the Preferred Embodiment is directedto use in the production of paper pulp goods with the industrial dryerthat is the subject matter of U.S. Pat. No. 5,105,558. Obviously, othersources of superheated steam may be used with the present invention.This description is by way of example and is not meant to be limit thescope of the present invention.

[0023] A direct-contact steam-to-water heat exchanger in accordance withthe present invention is generally represented by the referencecharacter 10 in the figures and includes, as shown in FIG. 1, awhitewater heat exchanger 20, a freshwater heat exchanger 30, afreshwater sump 40, a whitewater sump 50, a superheated steam inlet 60,and a steam plenum 62.

[0024] With reference to FIG. 1, a superheated steam inlet 60distributes superheated steam from an industrial dryer (not shown)through a forked steam plenum 62 to both a whitewater heat exchanger 20and freshwater heat exchanger 30. Each of these heat exchangers has agenerally cylindrical shape, and the superheated steam enters each heatexchanger near the bottom of the cylinder through exchanger steam inlets24, 34 respectively. The superheated steam entering each heat exchangeris regulated by a damper 61 a, 61 b that is present between the plenum62 and each exchanger steam inlet 24,34. These dampers are typically ofthe electronically controlled “butterfly-valve” type.

[0025] The freshwater heat exchanger 30 has a freshwater inlet 32 thatfeeds a freshwater spray nozzle 35. After passing through the freshwaterspray nozzle 35, the freshwater flows downward through the freshwaterheat exchanger 30 and eventually collects in a freshwater sump 40.Between the freshwater spray nozzle 35 and the freshwater sump 40,“packing” 36 is stacked. This packing 36, sometimes known as“tellerettes” or “saddles,” consists of cylinder segments that haverectangular portions removed in a brick-like pattern from their surface.On this inside of these hollow cylinder segments are arched portions ofmetal. This packing 36 is present to increase the distance the surfacearea which the falling freshwater must travel on its downward path tothe freshwater sump 40.

[0026] With reference to FIG. 2, the inside of the whitewater heatexchanger 20 is shown. Whitewater enters into the whitewater heatexchanger 20 through a whitewater inlet 22 which is positioned near thetop of the whitewater heat exchanger 20. The whitewater then is sprayedthrough a whitewater spray nozzle 18 toward an upper most baffle traywhich is one of nine similar semicircular baffle trays 25. Each baffletray 25 is fastened along its arc to the inside wall of the heatexchanger and is made so as to cover slightly more than half of thecross sectional area of the heat exchanger 20. The trays are positionedhorizontally, though in other embodiment s they can be tilted downward(i.e., the body-spanning straight-edge lies along the lowest point)slightly. Each of these baffle trays 25 is positioned at a differentheight within the whitewater heat exchanger 20, and the distance betweenadjacent baffle trays 25 drops from bottom to top to maintain thevelocity of the superheated steam and to keep heat transfer coefficientsup. The baffle trays 25 alternate in orientation: each baffle tray 25 isrotated about the vertical centerline of the whitewater heat exchanger20 through an angle of about 180 degrees. By this arrangement any twoadjacent baffle trays 25 cover the entire cross sectional are of thewhitewater heat exchanger 20. Each of the baffle trays 25 has a verticalwall, the outlet weir 17, along its body-spanning straight-edge.Whitewater sprayed from the spray nozzle 18 pools upon the uppermostbaffle tray and the baffle tray immediately below. Two rows of holes 16which are formed through each baffle tray 25 near the outlet weir 17allow some of this pooled water to flow downward to be caught by thenext baffle tray 25. When the flow of whitewater through the whitewaterheat exchanger 20 exceeds the capacity (designed to be about 50% ofdesigned flow through the whitewater heat exchanger) of the drain holes16, the water flows over the outlet weir 17 and down toward the nextbaffle plate 25, and in so doing forms a continuous water curtain. Atlow flows when all of the water is flowing through the drain holes 16, awater curtain still develops but in this case the curtain is notnecessarily continuous. The superheated steam which is traveling upwardthrough the heat exchanger 25 is constrained to travel through the watercurtains and it is the passing of the steam through these water curtainsthat effects the bulk of the heat transfer within the whitewater heatexchanger 20.

[0027] With regard to the whitewater heat exchanger 20, the superheatedsteam that has passed through the plenum 62 and that has been admittedby the damper 61 enters through the 5 whitewater heat exchanger steaminlet 24. The superheated steam then rises through the whitewater heatexchanger due to a pressure gradient present between the steam inlet 24and the steam outlet 19. A fan (not shown) located along the exhaustpipe 70 facilitates in the creation of this pressure gradient. Achevron-type mist eliminator (not shown) is near the steam outlet 19 toreduce water carry-over to the fan. A water wash of approximately onegallon per minute (1 gpm) is placed on top of the mist eliminator towash away any solids or deposits back down to the whitewater steamexchanger 20.

[0028] With reference to FIG. 3, a plan view of one of the baffle trays25 is shown. Two rows, one offset from the other, of drain holes 16 areshown near the outlet weir 17. With reference to FIG. 4, a fullcircumferential tray ring 47 is shown. Such a tray ring 47 is providedin the whitewater heat exchanger 20 at the position of the topmostbaffle tray 25 and the lowermost baffle tray 25. These tray rings 47allow for, after the removal of the baffle plates 25, packing (notshown) to be used in the whitewater heat exchanger 20 such a change isdesired.

[0029] With reference to FIG. 5, an edge view of one of the baffle trays25 is shown. The outlet weir 17 is shown having a 90 degree V-notchpatten across the top edge of the outlet weir 17. This patternfacilitates the stable operation of the whitewater heat exchanger 20 atlow to moderate flows.

[0030] The previous description of the Preferred Embodiment is by way ofexample and does not define the scope of the present invention. As willbe apparent to those skilled in the art, various changes andmodifications may be made to the apparatus of the present inventionwithout departing from the spirit and scope of the present invention asrecited in the appended claims and their legal equivalent.

What is claimed is:
 1. An apparatus for heating a whitewater supply,said apparatus comprising: a superheated steam inlet receiving steamfrom a superheated steam source; and a whitewater heat exchangerreceiving a flow of superheated steam from said superheated steam inlet,said whitewater heat exchanger also receiving a flow of whitewater;wherein said supply of whitewater receives heat directly from saidsuperheated steam within said whitewater heat exchanger.
 2. Theapparatus of claim 1 wherein said whitewater heat exchanger includes: aheat exchanger body having a longitudinal axis; a plurality of baffleplates, each of said plurality being substantially perpendicular to saidlongitudinal axis; a superheated steam inlet on said heat exchangerbody; a superheated steam outlet on said heat exchanger body; awhitewater inlet on said heat exchanger body; and a whitewater outlet onsaid heat exchanger body; wherein said flow of superheated steam enterssaid whitewater heat exchanger through said superheated steam inlet andexits through said superheated steam outlet, wherein said whitewaterflow enters said whitewater inlet and exits through said whitewateroutlet, and wherein said whitewater flow mixes directly with saidsuperheated steam flow and is thereby heated.
 3. The apparatus of claim2 wherein each of said plurality of baffle plates is rotated about saidlongitudinal axis with respect to each adjacent baffle plate of saidplurality of baffle plates.
 4. The apparatus of claim 3 wherein saidheat exchanger body is cylindrical.
 5. The apparatus of claim 4 whereineach one of said plurality of baffle plates is semi-circular with abody-spanning straight-edge.
 6. The apparatus of claim 3 wherein eachone of said plurality of baffle plates has a lip along saidbody-spanning straight-edge.
 7. The apparatus of claim 6 wherein saidlip is substantially parallel to said longitudinal axis.
 8. Theapparatus of claim 7 wherein each one of said plurality of baffle platesfurther comprises a first plurality apertures disposed therethrough. 9.The apparatus of claim 8 wherein said first plurality of apertures isarranged in a first row along said lip.
 10. The apparatus of claim 9wherein each of said first plurality of apertures is spaced an identicaldistance from an adjacent aperture of said first plurality of apertures.11. The apparatus of claim 8 further comprising a second plurality ofapertures disposed therethrough.
 12. The apparatus of claim 11 whereinsaid second plurality of apertures is arranged in a second row parallelto said first row.
 13. The apparatus of claim 2 further comprising afreshwater heat exchanger.
 14. The apparatus of claim 13 wherein saidfreshwater heat exchanger comprises: a freshwater heat exchanger bodyhaving a freshwater inlet disposed therethrough; a freshwater outletdisposed through said freshwater heat exchanger body; a superheatedsteam inlet disposed through said freshwater heat exchanger body; and asuperheated steam outlet disposed through said freshwater heat exchangerbody, wherein said supply of freshwater receives heat directly from saidsuperheated steam within said freshwater heat exchanger.
 15. A steamcondenser comprising: a superheated steam inlet receiving steam from asuperheated steam source; a superheated steam plenum attached to saidsuperheated steam inlet: a whitewater heat exchanger receiving connectedto said superheated steam plenum and receiving a first flow ofsuperheated steam from said superheated steam plenum, said whitewaterheat exchanger also receiving a flow of whitewater; wherein said supplyof whitewater receives heat directly from said superheated steam withinsaid whitewater heat exchanger; and a freshwater heat exchangerconnected to said superheated steam plenum and receiving a second flowof superheated steam from said superheated steam plenum, said freshwaterheat exchanger also receiving a flow of freshwater; wherein said supplyof freshwater receives heat directly from said superheated steam withinsaid freshwater heat exchanger.
 16. The apparatus of claim 15 whereinsaid whitewater heat exchanger includes: a whitewater heat exchangerbody having a longitudinal axis; a plurality of baffle plates, each ofsaid plurality being substantially perpendicular to said longitudinalaxis; a superheated steam inlet on said heat exchanger body; asuperheated steam outlet on said heat exchanger body; a whitewater inleton said heat exchanger body; and a whitewater outlet on said heatexchanger body; wherein said flow of superheated steam enters saidwhitewater heat exchanger through said superheated steam inlet and exitsthrough said superheated steam outlet, wherein said whitewater flowenters said whitewater inlet and exits through said whitewater outlet,and wherein said whitewater flow mixes directly with said superheatedsteam flow and is thereby heated.